1. Field of the Invention
The present invention employs a unique ultrasound apparatus to more accurately determine the maximum backfat in any one of a variety of animals even though the number and thickness of their backfat layers are different because of their different species, breeds, ages and weights. As meat packers make their profits from selling lean meat, it is vital for them to purchase live animals, e.g. pigs, that contain a minimal amount of backfat. It is therefore vital that they employ an apparatus that will more accurately measure the backfat of the animals they purchase than any backfat measuring apparatus that is presently available for this purpose.
2. Description of the Prior Art
Prior art backfat measuring devices have used a single ultrasonic beam known as A-mode technology and a swept beam known as B-mode technology. Prior A-mode methods have used simple peak detection and peak counting techniques of the echo signals generated by the fat layers of livestock to determine the total depth of their fat cover. The advantage of A-mode is its lower cost and lower system complexity. Existing systems have also used visual user interpretation of the signal waveforms. B-mode systems have used user interpretation, or some automated means involving lateral pattern recognition. However, B-mode systems with this feature currently require an external computer interface and analysis equipment. Therefore, these B-mode systems are too costly and too complex to satisfy present-day purchasers of such equipment.
Present day A-mode systems fail to completely solve this problem because when an input signal is transmitted into the backfat of an animal the resulting amplitude of the reflected peak of the signal that is detected by present day techniques are often in error due to the variability of the tissue reflection strength, causing either false returns if the detection level is too low, or missed returns if the peak detection threshold is too high. Further, in most livestock species, especially pork, the number of fat layers increases with increasing fat thickness. Therefore a peak-counting procedure can be in error. In addition, the final tissue interface between fat and muscle, which is the most important one in terms of fat thickness measurement, is generally not a distinct, thin layer, but an extended region of connective tissue. The peak of the ultrasound signal returned from this type of layer does not adequately quantify the extent of the layer, which leads to errors unacceptable in the present-day market.
Prior art systems, for example Carlson (U.S. Pat. Nos. 4,359,055 and 4,359,056), use peak detection circuitry to find the location of the peak of each echo signal returned as a result of ultrasonic pulses that have been transmitted into the animal through a transducer. However, there is an error in this approach because this approach identifies the peak of the echo signal as the depth to the fat/loin interface, whereas the true fat/loin interface is at a substantial percentage below the peak. The fact that the fat/loin interface is below the peak was shown to be true in an accreditation test by the National Swine Improvement Federation in January 1995. The federation certified operators using the system disclosed herein which uses this below-the-peak measurement approach to have a high degree of accuracy in backfat measurements when compared to actual carcass data.